Show existing tree adoptions more prominent

[joergreichert]

Current state: Tree profile page doesn't show when it is already adpoted by someone else. Only the extra adotption filter shows all trees adopted.

Motivation: As a user I want see in the tree profile (maybe even in the map itself as a marker icon decorator) when a tree has been already adopted, so he/her known someone is already taking care of the tree.

Future state: A marker decorator icon shows when a tree has been already adopted and tree details view shows who / how many people adopted the tree.

[joergreichert]

Proposal in working group meetup: Show a (green) heart icon (surrounding, icon decorator) for adopted trees (different color for icon when own adoption),